The present invention is directed to wireless radio frequency modems and, more specifically, to a method and apparatus for extending battery life in an RF wireless modem by automatically commanding the RF modem into a low power, auto-sleep-no-coverage mode when coverage is not available.
Current wireless radio frequency (xe2x80x9cRFxe2x80x9d) modems that cooperatively operate with a host computing device (xe2x80x9chost computerxe2x80x9d) typically include: (1) a radio portion, also called an RF front end or an RF head; (2) a modulator/demodulator portion, also called a baseband processing unit or baseband chip; (3) a central processing unit (xe2x80x9cCPUxe2x80x9d) or processor; (4) a memory; and (5) an interface. These modems typically operate using software code to communicate between a user and a base station. The above modem components collectively operate during a wireless communications process to receive an electromagnetic RF signal in a receive mode, wherein the RF signal contains information to be extracted from the received RF signal, and in a transmit mode, wherein the components work collectively to transmit an electromagnetic RF signal, and the RF signal contains the information to be transmitted. Moreover, during the receive and transmit modes, the modem components collectively operate to perform three principal modem functions: RF conversion, baseband processing and protocol stack control.
Typically during RF conversion, the RF head receives the RF signal during the receive mode and converts that RF signal into a modulated baseband analog signal and, during the transmit mode, the RF head converts a modulated baseband analog signal into an RF signal for transmission. During baseband processing, the baseband processing unit in the receive mode demodulates the modulated baseband analog signal by extracting a plurality of data bits that correspond to the information being received. In the transmit mode, the baseband processing unit generates the modulated baseband analog signal for processing by the RF head.
As part of the above wireless communications process, data bits being transmitted are wrapped with protocol bits of data to facilitate transmission, routing, and receiving of the data bits. Likewise, this protocol data must be removed to accurately reproduce, in the receiving RF modem, the data that was sent. The adding or stripping of the protocol bits, also called protocol stack control, is generally performed by the processor in the RF modem under the control of a protocol stack software program stored in the RF modem""s memory. Finally, the interface feeds the data bits from the host computer to the RF modem for processing and transmission, and feeds to the host computer the reproduced data bits that were extracted from the received RF signal.
The host computer may typically be a battery powered laptop or palmtop computer, or a Personnel Digital Assistant (PDA), such as a Jornada 545 from Hewlett Packard Co., an IPAQ computer from Compaq Corporation, a Palm III or Palm V from Palm Corp. or a Visor from Handspring Corp. The host computer may also be other types of battery powered devices such as a point of sale terminal, a wireless meter reader, a wireless sensor transmitter or some other computing system. Typical interfaces between the wireless RF modem and the host computer are RS-232, USB, Parallel Port, IrDa, PCMCIA, Flash, Compact Flash, or a low voltage serial interface. However, other interfaces are also used, including a variety of other standard or proprietary interfaces.
Moreover, there are many wireless RF standards that must be considered in the design of any wireless RF modem. Some examples include: circuit switched commercial telecommunications standards including AMPS, CDMA (IS95A and B), and GSM; packet switched standards including CDPD, 1XRTT, GPRS, EDGE, W-CDMA and UMTS; and proprietary wide area wireless networks such as Metricom, Re-Flex, FLEX, Mobitex, and ARDIS.
Current technologies are primarily circuit-switched, meaning a continuous circuit transmission allows the network to route continuous data to a single location. Circuit-switched data requires a dedicated radio channel even when no data is being sent. Packet-switched data does not work the same way as circuit-switched data. With packet-switched data, the modem can send bursts and receive bursts of data. Each burst contains a sequence identification number allowing the regeneration of the blocks of data once all data is sent. A radio channel is occupied only for the duration of the data transmission instead of being dedicated to one user continuously.
A brief overview of some of the above standards is as follows. However, details of many of these standards are available through industry organizations. CDPD (Cellular Digital Packet Data) is a packet-data wireless technology developed by ATandT Wireless Services and other cellular carriers based on Internet Protocol (IP) networking. The CDPD wireless communication system exists to allow mobile users access to the Internet via a wireless link. The specification for this system is entitled xe2x80x9cA Cellular Digital Packet Data System Specificationxe2x80x9d (the xe2x80x9cCDPD Specificationxe2x80x9d) Release 1.1 dated Jan. 19, 1995 and is available from Wireless Data Forum, Suite 800, 1250 Connecticut Ave. N.W., Washington, D.C. 20036. CDPD is deployed as an overlay to analog cellular networks. It enables analog networks such as AMPS (Advanced Mobile Phone Service) to carry packetized data alongside voice. It is primarily used to transmit brief messages, read e-mail, and perform some web browsing for, e.g., wireless enabled Personal Digital Assistants and RF wireless modem equipped laptops. CDPD uses either idle voice channels or dedicated data channels depending on network configuration. However, since the modem never makes an actual xe2x80x9cphone call,xe2x80x9d the channel becomes immediately available for other data users after the transmission. At the switching center, packet services interconnect with the Internet or directly with corporate intranets using traditional networking methods such as frame relay. Service, available in most major cities in the US and Canada, is provided by major cellular companies.
GPRS is another kind of packet-switched data technology that is being developed for GSM networks. 1XRTT is a packet-switched data technology that uses CDMA techniques. Ricochet is a packet-switched data network operated by Metricom in the unlicensed ISM 902 MHz to 928 MHz band. EDGE, 3G, W-CDMA, and UMTS plus others are all planned to use packet data.
In the battery-operated host computing devices described above, e.g., a mobile unit, it is important to conserve power as much as possible. Therefore, in many of the above wireless air standards, and in CDPD in particular, there is an in-coverage sleep mode (or xe2x80x9cstatexe2x80x9d) detailed in the specifications. The RF wireless modem in the mobile unit coordinates a sleep-mode timer value with a base station controller and then issues a command to the control circuitry within the modem to direct the modem into a sleep mode with the parameters set by the negotiation. This in-coverage sleep mode is very efficient and effective. Unfortunately, if the mobile unit moves out of the coverage area while it is in a sleep mode then a lot of time and power is spent by the modem in searching and trying to re-establish communications with a base station controller. The battery power consumed while performing this search greatly reduces the mobile unit""s standby time, particularly when compared to that enjoyed when the unit is within its service area where a low power mode can be used.
For CDPD for example, most of the operation of the RF wireless modem is defined in the CDPD Specification in two relevant sections. The first section, Section 6.8 in pub. 403 at pp. 58 through 62, describes a sleep mode procedure for in-coverage usage. The in-coverage sleep mode is a coordinated low power mode available and requested from the current CDPD base stations. This in-coverage mode is coordinated in that the registered modem device and the base station to which it is registered coordinates when the mobile device will enter into this low power mode so that data communication can still take place when the device wakes up again. The CDPD Specification defines this and a series of timing parameters that are used by the device to maintain this coordination.
The following description is taken directly from the CDPD Specification at page 58. The term xe2x80x9cM-ESxe2x80x9d means Mobile End Systems; xe2x80x9cTEIxe2x80x9d means Temporary Equipment Identifier; and xe2x80x9cMDLxe2x80x9d means Mobile Data Link in the following quoted text from the CDPD Specification:
xe2x80x9cSleep mode is an optional mode of operation that may be requested by an M-ES during the data link establishment procedure. Sleep mode is intended to assist power conservation strategies in the M-ES. General operation of sleep mode permits an M-ES to disable or powerdown its receiver and associated circuitry. The procedure operates in the multiple frame established state as follows. If there are no frames being exchanged on the data link connection after a period of time defined by timer T203, the data link connection may be placed in the TEI-sleep state. The network shall not attempt to transmit information destined for the M-ES while in the sleep state. If after entering the sleep state, new frames become pending initial transmission, the network shall broadcast at periodic intervals a message containing a list of TEIs for which forward channel data is pending. M-ESs are expected to wake up at periodic intervals to determine if data for them is pending and notify the network when they are willing to receive. The M-ES may exit the sleep state at any time.
6.8.1 Negotiation for Use of Sleep Mode Use or non-use of sleep mode supervision is indicated by the IDLE TIMER Parameter Octet during the TEI Assignment procedure initiated by the M-ES. Non-use of sleep mode supervision is selected by negotiating a value for timer T203 of 0.
6.8.2 Idle Timer T203. Timer T203 represents the maximum time allowed without frames being exchanged on the data link connection. On the user side, timer T203 is started or restarted upon transmission of a Data Link Layer frame (of any type) on the reverse channel. On the network side, timer T203 is started or restarted upon receipt of a Data Link Layer frame (of any type) on the reverse channel.
6.8.3 Expiry of Timer T203. If timer T203 expires, the data link entity shall: * Enter the TEI-sleep state *Issue a MDL-SLEEP indication primitive on the user side. The layer management entity may take power conserving measures (e.g., disabling the radio receiver or other non-essential portions of its circuitry). The details of operation while in this state are implementation dependent.xe2x80x9d
The second relevant section in the CDPD Specification is Section 3.3.9 in pub. 405 at pp. 28 through 31. This section describes the theory of operation that is assumed when the device is outside coverage. This theory of operation describes a channel scanning algorithm that attempts to find service again. Although not specifically mandated, it is assumed that the unit would stay in this channel scanning mode until coverage is found again or the unit is turned off by the mobile user. Unfortunately, since the modem is constantly channel scanning while out of coverage, it is constantly tuning and retuning the synthesizers to attempt to xe2x80x9clock-onxe2x80x9d to CDPD service. This means that the modem is consuming a relatively large amount of current from the battery while it searches for service on these channels and will continue to consume this current until service is detected again, the unit is shut off, or the unit exhausts its battery.
The following description is taken directly from the CDPD Specification at page 28. The term xe2x80x9cRRMExe2x80x9d means Radio Resource Management Entity and xe2x80x9cSPNIxe2x80x9d means Service Provider Network Identifier:
xe2x80x9cThe RRME shall execute this procedure on the search for a CDPD channel stream when the Adjacent Cell Scan procedure is unsuccessful or has insufficient information. These conditions include:
Power up (initial acquisition)
Unacceptable SPNI, SPI or WASI on the current cell or adjacent cells
Unsuccessful after exhausting the RF channel list of adjacent cells or after an implementation dependent time. The order in which RF channels are searched shall be implementation dependent.
Examples of possible search algorithms include but may not be limited to:
Sequential search of all possible channels, or based on the A/B side preference indicated by the WASI values of acceptable WASIs.
A search order making use of knowledge of the allocation of channels within a cell (e.g., in steps of 21 channels)
A search criteria making use of knowledge gained by examining RSSI or data found on AMPS control channels
A search order giving priority to allocated channels in cells previously acquired by the M-ES
A search order based on allocated channels in cells frequently used by the M-ES.
The RRME shall perform the following procedure:
a. Issue a PH-OPEN.request primitive
b. Determine the RSSI via a PH-RSSI.indication primitive
c. If the RSSI is determined to be unacceptable, via implementation dependent criteria, the RRME shall select another channel
d. Issue a MAC-OPEN.request primitive
1. If the response is a MAC-CLOSE.indication primitive, indicating the MAC layer was unable to synchronize with a CDPD channel stream on the new RF channel, the RRME shall search another channel
2. If the response is a MAC-OPEN.confirm primitive, the RRME shall examine the quality of the channel as follows:
A. The RRME shall examine the block error rate of the channel, based on the MAC-STATUS.indication primitive, for a time which shall be implementation dependent. If the block error rate is determined to be above a threshold which shall be implementation dependent, then the RRME shall search another channel.
B. The RRME may optionally determine other measurements, such as the symbol error rate, and the sync word error rate.
If the block error rate and other implementation-dependent criteria are acceptable, then the RRME shall terminate the search.
3. On receipt of a CHANNEL STREAM IDENTIFICATION message, the RRME shall then execute the Cell Transfer procedure defined in Section 3.3.12.xe2x80x9d
Many manufacturers have implemented the low power mode for in-coverage modem operation as specified above in the CDPD Specification. However, no current modem implementations provide similar battery life outside of the coverage area to that achieved while in full coverage. Similar problems exist with many of the other wireless standards and systems.
What the industry needs is a way for an RF wireless modem to go into a sleep mode while in a non-coverage area and still be responsive when the mobile user enters a coverage area.
The present invention is directed at addressing the above-mentioned shortcomings, disadvantages, and problems of the prior art. The present invention provides for a method for causing a radio frequency (xe2x80x9cRFxe2x80x9d) modem to operate in a low power state when said modem is unable to register itself with a base station controller within said modem""s coverage area, said modem comprising a central processing unit and a first and second timer, said method comprising the steps of: (a) setting a time duration for said first timer, wherein the time duration of said first timer is the maximum amount of time that said modem will attempt to register with a base station controller before entering into a low power state; (b) setting a time duration for said second timer, wherein the time duration of said second timer is the amount of time that said modem will operate in said low power state; (c) detecting that a connection to a base station controller is lost, and causing said first timer to start; (d) attempting to register said modem with base station controller; (e) causing said modem to operate in a normal modem active state if said modem registers with said base station controller before said first timer times out, and causing said second timer to start if said modem has failed to register with said base station controller at the point when said first timer times out; (f) causing said modem to operate in said low power state during the duration of said second timer; and (g) causing said modem to awaken from said low power state when said second timer times out and to return to step (c). Preferably the RF modem implementing this method operates using a Cellular Digital Packet Data standard. In addition, the timers used are preferably software programmable, said first timer is preferably set to a time to allow said modem to scan all available channels to locate service and said second timer is set to a time that is a multiple of said first timer. Moreover, the method of claim 1, may further comprise notifying an attached host computing device when said modem enters into said low power state and when said modem awakens from said low power state.
The present invention also provides for a method for causing a radio frequency (xe2x80x9cRFxe2x80x9d) modem to operate in a low power state when said modem is unable to register itself with a base station controller within said modem""s coverage area, said modem comprising a central processing unit, a first, second and third timer and a counter, said method comprising the steps of: (a) setting a time duration for said first timer, wherein the time duration of said first timer is the maximum amount of time that said modem will attempt to register with a base station controller before setting said counter and entering into a low power state; (b) setting a time duration for said second timer, wherein the time duration of said second timer is the amount of time that said modem will operate in said low power state; (c) setting a time duration for said third timer, wherein the time duration of said third timer is the maximum amount time said modem will attempt to register with a base station controller before returning to said low power state; (d) detecting that a connection to a base station controller is lost, and causing said first timer to start; (e) attempting to register said modem with a base station controller; (f) causing said modem to operate in a normal modem active state if said modem registers with said base station controller before said first timer times out, and causing said counter to be set if said modem has failed to register with said base station controller at the point when said first timer times out, wherein said counter is the maximum number of times said modem will operate in said low power state before it returns to step (d); (g) starting said second timer; (h) causing said modem to operate in said low power status during the duration of said second timer; (i) decrementing the value of said counter; (j) detecting if the value of counter said counter is zero; (k) causing said modem to awaken from said low power state and to return to step (d) if said counter value is zero, and causing said modem to awaken and said third timer to start if said counter value is greater than zero; (l) attempting to register said modem with a base station controller; (m) causing said modem to operate in a normal modem active state if said modem registers with said base station controller before said third timer times out and to return to step (f) if registration is subsequently lost, and causing said modem to return to step (g) if said modem has failed to register with said base station controller at the point when said third timer times out. Preferably the RF modem implementing this method operates using a Cellular Digital Packet Data standard. In addition, the timers and the counter used are preferably software programmable, said first timer is preferably set to a time to allow said modem to scan all available channels to locate service, said third timer is set to allow said modem to scan a subset of said available channels that is a list of preferred channels, and said second timer is set to a time that is a multiple of said third timer. Moreover, the method of claim 1, may further comprise notifying an attached host computing device when said modem enters into said low power state and when said modem awakens from said low power state.
The present invention also provides for a wireless radio frequency (xe2x80x9cRFxe2x80x9d) modem, said modem having an antenna, an RF head, a baseband processing unit, a memory for storing modem operating system instructions, and a central processing unit (xe2x80x9cCPUxe2x80x9d) for attempting to register said modem with a base station controller within said modem""s coverage area and for detecting that a connection to a base station controller has been lost, the improvement comprising: a first timer coupled to said CPU that is set to a time duration that is the maximum amount of time that said modem will attempt to register with a base station controller before operating in a low power state; means coupled to said first timer for starting said first timer, said means responsive to a detection that a connection to a base station controller has been lost; a second timer coupled to said CPU that is set to a duration that is the amount of time that said modem will operate in said low power state; and means coupled to said second timer for starting said second timer, said means responsive to said first timer timing out; wherein said CPU is operative under the control of said operating system instructions to cause said modem to operate in a normal modem active state when said modem registers with a base station controller before said first timer times out, said CPU is further operative to cause said modem to operate in said low power state for the time duration of said second timer when said modem is unable to register itself with a base station controller before said first timer times out, and said CPU is further operative to cause said modem to awaken from said low power state and attempt to register with a base station controller at the point when said second timer timers out.
Finally, the present invention provides for a wireless radio frequency (xe2x80x9cRFxe2x80x9d) modem, said modem having an antenna, an RF head, a baseband processing unit, a memory for storing modem operating system instructions, and a central processing unit (xe2x80x9cCPUxe2x80x9d) for attempting to register said modem with a base station controller within said modem""s coverage area and for detecting that a connection to a base station controller has been lost, the improvement comprising: a first timer coupled to said CPU that is set to a time duration that is the maximum amount of time that said modem will attempt to register with a base station controller before operating in a low power state; means coupled to said first timer for starting said first timer, said means responsive to a detection that a connection to a base station controller has been lost; a second timer coupled to said CPU that is set to a duration that is the amount of time that said modem will operate in said low power state; means coupled to said second timer for starting said second timer, said means responsive to said first timer timing out; a counter coupled to said CPU that is set to a value that is the maximum number of times said modem will operate in said low power state before restarting said first timer and attempting to register said modem with a base station controller; means coupled to said counter for setting and starting said counter, said means responsive to said first timer timing out; means coupled to said counter for detecting the value of said counter; a third timer coupled to said CPU that is set to a time duration that is the maximum amount of time that said modem will attempt to register with a base station controller before re-entering said low power state after sleeping for a time determined by said second timer; and means coupled to said third timer for starting said second timer, said means responsive to a detection that said counter is greater than zero; wherein said CPU is operative under the control of said operating system instructions to cause said modem to operate in a normal modem active state when said modem registers with a base station controller before said first timer times out, said CPU is further operative to cause said modem to operate in said low power state for the time duration of said second timer when said modem is unable to register itself with a base station controller before said first timer times out, said CPU is further operative when said counter value is zero to cause said modem to awaken from said low power state and to attempt to register with a base station controller at the point when said second timer timers out, said CPU is further operative to cause said modem to operate in a normal modem active state when said modem registers with a base station controller before said third timer times out, and said CPU is further operative to cause said modem to operate in said low power state for the time duration of said second timer when said modem is unable to register itself with a base station controller before said third timer times out.
An object of the present invention is to provide for a method and apparatus for extending battery life in an RF wireless modem by automatically commanding the RF modem into a low power, auto-sleep-no-coverage mode when coverage is not available.
A key advantage of the present invention is that the auto-sleep-no-coverage mode timing is configurable solely through software parameters in the operating system of the modem. Therefore, the invention does not require any change to the base station control software.
Another advantage of the present invention is that it conforms to the Cellular Digital Packet Data (CDPD) Specification and improves the standby time one would otherwise achieve by balancing the modem response time target, upon returning to a coverage area, with the standby time target. By using this invention, the standby time of the device outside the coverage area can approach the standby time of the device within the coverage area. Whereas, without this invention the standby time outside the coverage area is significantly reduced compared to the standby time within the coverage area. Thus, the present invention provides users with consistency of modem operational battery life in both coverage cases.